1. Field of the Invention
The present invention relates to an image forming apparatus using continuous paper supply.
With the recent progress in the art of high speed computer systems, a printer, as an output apparatus of the high speed computer system, is required to ensure high speed operation and high reliability of the printing operation. An image forming apparatus, such as an electrophotographic printer, etc. is expected to meet such requirements. Electrophotographic printers are widely used now, in the form of laser beam printers and LED array printers. These printers have a feature that printed papers may be output at a high speed.
The electrophotographic printer, such as a laser beam printer or an LED array printer, forms a toner image on a recording sheet by executing the processes explained in the following. First, a photosensitive drum, as a toner carrying member, is uniformly charged in either a positive or a negative polarity. Next, the photosensitive drum is exposed depending upon input image information and thereby an electrostatic latent image is formed on such photosensitive drum.
An electrostatic latent image on the photosensitive drum is developed by using a toner which is charged in the same polarity as the charged polarity of the photosensitive drum. That is, since a toner is attached with an electrostatic force on an exposed area of the photosensitive drum, a toner image can be formed on the photosensitive drum. The toner image on the photosensitive drum is then transferred onto a recording sheet, usually by a transfer corona, in a transfer station. As the recording sheet, a continuous paper or a cut sheet is used. As the continuous paper, a rolled paper or a folded sheet can be used.
2. Description of the Related Art
A paper transfer mechanism provided in an electrophotographic printer of a prior art mechanism, using paper from a continuous paper supply is provided with a transfer guide mechanism for contacting the paper of the continuous paper with the photosensitive drum and for separating the paper of the continuous paper from the photosensitive drum. This transfer guide mechanism is provided with a means for equalizing the paper transfer route length when the continuous paper is closely contacted with the photosensitive drum and when the continuous paper is separated therefrom. Such paper transfer mechanism has been published in the Japanese Laid-Open Patent No. SHO 53-21934.
A paper transfer mechanism different from the paper transfer mechanism disclosed in the above Japanese Patent was made public in the Japanese Laid-Open Patent No. SHO 50-34543. This paper transfer mechanism is provided with a movable guide which executes forcible separation of the continuous paper from the photosensitive drum by pushing the continuous paper toward the upstream side of the transfer section, taken in view of the photosensitive drum.
The paper transfer apparatus of the prior art comprising the transfer guide means explained above has a problem in that the configuration of the transfer guide means is rather complicated. Meanwhile, the paper transfer mechanism comprising the movable guide causes the continuous paper to be loosened, by as much as the distance moved by the movable guide during the transfer process.
When the continuous paper is loosened, it scrubs the photosensitive drum or contacts with an upper paper guide. This may happen during an operation in which the continuous paper comes in contact with the photosensitive drum or during a transfer operation. Thereby, there is a possibility that toner is separated from the continuous paper and/or the photosensitive drum, or that a surface of the photosensitive drum is damaged.